Cooler inlet device



Dec. 12, 1967 T LLW ET AL 3,357,435

COOLER INLET DEVICE Filed April 21, 1965 2 Sheets-Sheet l INVENTORSThomas F. O'Sullivon Jon Kramer Karl Buschmann Hermon Meyer ArminSchweitzer ATTORNEYS Dem 12, 1967 F OSULLIVAN ET AL 3,357,485

COOLER INLET DEVICE 2 Sheets-Sheet Filed April 21, 1965 lNVENTORS ThomasF. O'Sullivon Jon Kramer Karl Buschmonn Herman Meyer Armin SchweHzer BY5133 72/21, 77km figanywmflu'a ATTORNEYS United States Patent COOLERINLET DEVICE Thomas F. GSullivan, Wilton, Conn, Jan Kramer, Voorschoten,Netherlands, and Karl Buschrnann, Neustadt an der Weinstrasse, andHerman Meyer and Armin Schweitzer, Ludwigshafen (Rhine), Germany,assignors to The Lummus Company, New York, N.Y., a corporationofDeiaware Filed Apr. 21, 1965, Ser. No. 449,849 7 Claims. (Cl. 165-174)This invention relates to apparatus for production of olefins, withspecial reference to ethylene, by thermal cracking of hydrocarbons. Itis known that olefinic hydrocarbons may be prepared by thermal crackingof gaseous or completely evaporable liquid hydrocarbons in metal tubes,ina mixture with steam, at temperatures above 750 C. This forms crackedgas rich in olefins, such as ethylene and propylene, and also containinghigher olefins, diolefins, and other cracking products. To preventsecondary reactions, the highly reactive gas mixture must be quicklycooled. This cooling is in practice accomplishedby direct injection ofcoolants, as for instance liquid hydrocarbons, into the reactionmixture, or by indirect cooling, e.g. with the aid of water, in acrackedgas cooler.

In general, to improve heat recuperation, indirect cooling is preferred.A disadvantage of indirect cooling, however, is that deposits of coke orother cracking products are often formed, especially in the connectingduct between the cracking furnace and the cracked gas cooler, or in theindividual cooling tubes of the cooler. These deposits increase thepressure difference in the system and interfere with the uniformdistribution of the hot cracked gas on the cooling surfaces. The plantmust then be shut down at longer or shorter intervals and the cokingproducts must be cleaned out.

The connecting duct (between the cracking furnace and the cracked-gascooler) used to deliver the cracked gas to the cooling tubes, is, ingeneral, so designed that it gradually widens in diameter from thediameter of the cracking tube to the diameter of the cooler shell. Toavoid vortices, which prolong the residence time in this area andthereby cause secondary reactions, the angle of the cone to thedirection of flow must be kept as small as possible. When the coolershell is of large diameter, however, the connecting line forms arelatively large space, and it has been found that the long residencetime of the cracked gas in this space results in coking and decreasedolefin yield.

To prevent condensing heavy polymers on the gas side of the tube, thetube wall temperature must be controlled. When the cooling medium isevaporating water, the pressure must be very high (80 to 100atmospheres) to give the required tube wall temperature. One type ofexchanger construction well suited to such pressure is double tubebecause it does not require excessively thick shell or tube sheet.However, high severity pyrolysis requires extremely rapid cooling andvery low pressure drop across the cooler. This requires many paralleltubes of small diameter. A disadvantage of the double tube exchanger isthat tubes can not be located on close centers. When many parallel tubesare required the volume of the inlet device becomes large, forming anadiabatic reactor, the same as a large or long transfer line. Theadiabatic reaction reduces the temperature and causes coke formation,which increases the pressure drop and limits the length of operationbetween cleanings.

It is therefore an object of the present invention to provide animproved connector duct for heat exchangers wherein gas pressure is notsubstantially decreased, laminer flow is encouraged and vortices oreddys are discouraged.

3,357,485 Patented Dec. 12, 1967 Another object of the present inventionis to provide a connection duct for heat exchangers in which theresidence time of gases passing therethrough is minimized thus, in thecase of connectors between cracking heaters and quench coolers,minimizing secondary reactions and coke formation, and therebyincreasing yield.

Still another object of this invention is to provide an inlet device forthe inner tube side of high temperature, high pressure double tubeexchangers having many parallel tubes, that will have a very low volume.

Yet another object of this invention is to provide an inlet device whichwill convert the high velocity of the heater outlet (700 to 1000 feetper second) to the exchanger tube velocity (30() to 400 feet per second)with minimum pressure loss.

A still further object of this invention is to provide an inlet devicewhich will have very little or no dead space where the gas flow can forman eddy resulting in long residence time.

Various other objects and advantages of the invention will become clearduring the following description of two embodiments thereof, and thenovel features will be particularly pointed out in connection with theappended claims.

It has now been found that these disadvantages do not appear, and that.a particularly high olefin yield is obtained, if suitable baffies orguides are installed in the connecting piece between cracking tube andcracked-gas cooler. This prevents the velocity of the cracked gas in theconnecting piece from falling below its velocity at admission to thecooling tubes.

According to one embodiment of the invention, a diverter or baffle,preferably attached .to the cooler shell, is installed in the conicalconnecting duct between cracking tube and cracked-gas cooler. It isadvantageous for this diverter to have channels conducting the hotcracked gas to the individual cooling tubes. The diverter may alsoadvantageously have a hydrodynamically favorable shape so that atallpoints of the connecting duct the flow velocity of cracked gas shall notfall below the velocity at admission to the cooling tubes.

With the present double tube exchangers, tube spacing is over 3 timesthe gas tube I.D. giving an area of tube sheet approximately 10 timesthe flow area of the exchanger. Since the ar a of the heater outlettubes is about one half of the exchanger tubes, with conventional inletdevices the volume is approximately /3 that of the heater coil. Sincethis occurs at maximum temperature, the adiabatic reaction is rapid,having significant affect on the yields and promoting coke formation.The present invention reduces the volume to less than that of the heatercoil, thus reducing the adiabatic reaction to an insignificant amount.

The fluid velocity between the heater outlet to the exchanger inlet isinversely proportional to the flow area. With the areas resulting fromconventional construction the velocity is decreased by a factor oftwenty and then increased by a factor of ten. This results in a pressureloss of about 1.0 times the exit velocity head plus 0.5 times theentrance velocity head. This is about 2.8 p.s.i. for operatingconditions in use today, and would be greater for more severe conditionswhich can be obtained with use of this invention. This invention avoidsmost of the pressure loss, thus permitting operation at higher outletpressure or greater velocity in the exchanger or heater outlet, or anycombination of the three which results in improved product yield andgreater thermal efficiency.

Moreover, conventional inlet devices have abrupt changes in crosssections where the gas flow can develop eddies resulting in longresidence time for some of the gas. This permits polymerization anddehydrogenation 3 resulting in coke formation. The invention eliminatessuch areas thus preventing the undesired reactions.

It has been found advantageous to provide the diverter and connectingduct with good thermal insulation, so that the cracked gas is cooledonly when it reaches the cooling tubes. The connecting line betweencracking tube and the cooling tubes of the cracked-gas cooler should bekept as short as possible, sothat the cracked gas is distributed to thecooling tubes in the connecting duct as in a diffuser and Withouteddying.

A better understanding of the device of the invention will be gained byreferring to the accompanying drawings, wherein:

FIGURE 1 is a cross-sectional view of a first embodiment of theinvention;

FIGURE 2 is a cross-sectional view of a second embodiment of theinvention; and

FIGURE 3 illustrates two alternative constructions of the embodiment ofFIGURE 2.

With reference to FIGURE 1, the outlet pipe or flange from the crackingheater 2 is connected as by welding to a conventional cone-shapedconnecting duct 4 which is attached at flange 6 to a similar flange 8 onthe end of the quench cooler 10. The inner, gas side cooling tubes 12,are surrounded by outer water side tubes 13, and this assembly isconnected at each end of the cooler to suitable tube sheets 14. In thisembodiment, the diverter or baflie of the invention, indicated generallyat 16, comprises an outer conical shell 18, passages or tube extensions20 extending therethrough and connecting those of tubes 12 which arecovered by diverter 16 to orifices on the surface of shell 18 andinsulation 22 packed between the tube extensions 20 and the shell 18.The insulation is, of course, optional, and in certain applic'ations'airis sufiicient. The diverter 16 can be attached to exchanger in anyconvenient manner.

The diverter may be constructed as a unit assembly, with suitableprovision being made for attaching tube extensions 20 to the appropriatetubes 12, or tubes 12 may be extended, and shell 16 merely fittedthereover, the tubes then being cut oif to provide a flush orifice onthe surface.

As can be seen from FIGURE 1, gases passing through conical conduit 4will, due to diverter 16, lose much less pressure and have a moregenerally laminar flow in traversing the distance and entering tubes 12.

A somewhat different solution to the problem is illustrated in FIGURE 2,wherein parts similar to those in FIGURE 1 are indicated with primenumerals. In this embodiment, what in effect is done is provideextensions 20 for all of the tubes 12', extensions 20' terminating in asecond, dished tube sheet, indicated schematically at 24, of muchsmaller diameter than tube sheet 14. Tube sheet 24 may be as small, andmay be brought out as far, as it is possible to do and still have spaceavailable to accommodate the ends of tube extensions 20. Thus, the facepresented by tube sheet 24 to the gases is almost all tube openings andvery little supporting structure. The gases thus lose only a very smallamount of pressure in passing into extensions 20', and after that theylose no pressure or velocity in going into quench cooler 10.

An alternative arrangement involves bringing the tubes 20' into actualoutside contact and, rather than employing a tube sheet at all, merelyfilling the void space with a solid refractory material which bothprovides insulation and also excludes gas from what would otherwise bevoid space.

Such an arrangement is shown in FIGURE 3, which ineludes two variationsof the invention. On the right side, the tubes 20" are in actual contactwith refractory 22 filling the void space. On the left side of FIGURE 3,conduit 4 terminates at tube sheet 24, and tubes 20" are left exposed.

It will be noted that the embodiments of FIGURES 2 and 3 differ indegree rather than kind from the embodiment of FIGURE 1, in that theconical portion of diverter 16 is merely expanded to become part of duct4, and as a result all of the tubes 12 are covered.

It will be understood that various changes in the steps, materials,details and arrangements of parts, as described hereinabove, may be madeby those skilled in the art without departing from the scope of theinvention as defined in the appended claims.

What is claimed is;

1. A connector duct for the tube side of a heat exchanger thatcomprises:

a generally conical conduit connectable at its larger end to said heatexchanger around the periphery thereof;

a generally conical diverter axially located within said conduit andhaving its larger end connectable to said heat exchanger; and

a plurality of passages within said diverter coaxially connectable tothe individual tubes of said exchanger covered by the larger end of saiddiverter so as to be in fluid communication therewith, said passagesterminating at their opposite ends at the surface of said diverter.

2. The connector duct as claimed in claim 1, and additionally comprisingthermal insulation material within said diverter and surrounding saidpassages.

3. A connector duct for the tube side of a heat exchangcr thatcomprises:

a generally conical conduit connectable at its larger end to said heatexchanger around the periphery thereof; a plurality of extension tubescoaxially connectable to each of the tubes of said heat exchanger so asto be in fluid communication therewith, said tubes extending into thenarrower portions of said conduit, and

means securing the ends of said extension tubes within said narrowerportion of said conduit and adapted to maintain only said extensiontubes in fluid communication with said conduit.

4. The connector duct as claimed in claim 3, wherein said extensiontubes are in direct contact with each other and with said conduit at theend furthest from said heat exchanger and additionally comprisingrefractory insulation material between said contacting ends and saidheat exchanger and surrounding said extension tubes.

5. The connector duct as claimed in claim 3, wherein said securing meanscomprise a tube sheet.

6. In combination with a cracking heater and a shell and tube quenchcooler, a connector conduit that comprises:

a generally conical conduit connected at its larger end to said cooleraround the periphery thereof and connected at its smaller end to theoutlet of said heater:

a generally conical diverter axially located within said conduit andhaving its larger end connected to said cooler; and

a plurality of passages within said diverter, said passages being equalin number to and. in fluid communication with the individual tubes ofsaid cooler covered by said diverter at one end thereof and in fluidcommunication with the interior of said conduit at the other end.

7. The combination as claimed in claim 6, and additionally comprisingthermal insulation material within said diverter and surrounding saidpassages.

References Cited UNITED STATES PATENTS 2,862,694 12/1958 Lortz 1343,001,766 9/1961 Laist 165135 FOREIGN PATENTS 1,249,001 11/1960 France.

ROBERT A. OLEARY, Primary Examiner.

CHARLES SUKALO, Examiner.

1. A CONNECTOR DUCT FOR THE TUBE SIDE OF A HEAT EXCHANGER THATCOMPRISES: A GENERALLY CONICAL CONDUIT CONNECTABLE AT ITS LARGER END TOSAID HEAT EXCHANGER AROUND THE PERIPHERY THEREOF; A GENERALLY CONICALDIVERTER AXIALLY LOCATED WITHIN SAID CONDUIT AND HAVING ITS LARGER ENDCONNECTABLE TO SAID HEAT EXCHANGER; AND A PLURALITY OF PASSAGES WITHINSAID DIVERTER COAXIALLY CONNECTABLE TO THE INDIVIDUAL TUBES OF SAIDEXCHANGER COVERED BY THE LARGER END OF SAID DIVERTER SO AS TO BE INFLUID COMMUNICATION THEREWITH, SAID PASSAGES TERMINATING AT THEIROPPOSITE ENDS AT THE SURFACE OF SAID DIVERTER.